Disposable absorbent articles like baby diapers or adult incontinence briefs are well known in the art and commercially sold on a broad scale. Many of the commercially available diapers or briefs comprise an adhesive tape fastening system to secure the articles on a baby or an incontinent adult. The performance of the adhesive tape fastening system represents a key element for the functionality of such articles and therefore contributes to the commercial success of absorbent articles incorporating adhesive tape fastening systems.
Commercially available disposable absorbent articles generally comprise a liquid pervious topsheet, a liquid impervious backsheet, and an absorbent core placed between the topsheet and the backsheet.
The liquid impervious backsheet typically is a thin polyolefin film, almost always a polyethylene film. For economic, aesthetic and ecological reasons it is desirable to use films of a low caliper, for example, having an average nominal caliper of less than about 0.036 mm (1.4 mils).
The adhesive on the fastening tapes is selected such that the tapes will not fail in use. However, it is frequently desirable to unfasten the tapes to inspect the diaper for soiling for readjustment of the tapes. However, it is extremely difficult to formulate an adhesive for the fastening tapes that is sufficiently aggressive to prevent failure in use, yet allows peeling of the tape without tearing or stretching of the backsheet.
It is therefore a design objective for disposable absorbent articles to provide a reinforced landing area for the fastening tapes that allows use of an aggressive adhesive and yet at the same time allows unfastening of the tapes by peeling without stretching or tearing the backsheet.
For convenient reference, the surface of the backsheet facing the absorbent core of the absorbent article will be referred to as the internal surface of the backsheet. Similarly, the surface of the backsheet facing away from the absorbent core will be referred to as the external surface of the backsheet.
Numerous ways for reinforcing the landing zone of the backsheet have been proposed in the art.
U.S. Pat. No. 4,210,144, issued on Jul. 1, 1980 to Sarge III et al. proposes the use of a hot melt adhesive printed onto the backsheet in the landing zone for reinforcement of the landing zone. The hot melt adhesive may be applied as a continuous coating or as discrete lines or beads. The adhesive may be applied to the internal or external surface of the backsheet.
U.S. Pat. No. 4,296,750 issued to Woon et al. on Oct. 27, 1981 discloses a strip of adhesive applied to the internal surface of the backsheet in the landing zone.
U.S. Pat. No. 3,848,598 issued to Mesek on Nov. 19, 1974 discusses the reinforcement of disposable diapers having a closure system comprising either safety pins or adhesive tapes. The reinforcement materials in Mesek may be scrim or a strip of a polymer material having a high elastic modulus. The reinforcement material may be secured to either the internal or external surface of the backsheet, albeit that a "rough"reinforcement material is preferably secured to the internal surface of the backsheet.
European Patent Application 0 080 648A to Widlund published on Jun. 8, 1983 discloses the use of a smooth polymer film secured to the external surface of the backsheet. The polymer film is preferably made of polyester.
U.S. Pat. No. 5,024,672, issued Jun. 18, 1991 to Widlund discloses a similar reinforcement strip, however having an embossed surface. The reinforcement strip in Widlund is also placed on the external surface of the backsheet.
European Patent Application 0 287 767A to Koester published on Oct. 26, 1988 discloses a reinforcement strip secured to the internal surface of the backsheet. The reinforcement strip is made of a synthetic polymeric material and is adhered to the backsheet using a pressure sensitive adhesive.
U.S. Pat. No. B1 4,662,875 issued May 5, 1987 to Hirotsu & Robertson discloses a diaper having indicia printed on the backsheet for facilitating a symmetric application of the absorbent article. The indicia may be printed on a separate reinforcement strip which is secured to the internal surface or external surface of the backsheet.
The prior art in general relies on the use of expensive and stiff synthetic polymer materials, be it adhesive or polymer films, for use as a reinforcement member. The scrim material in Mesek appears to be an exception but scrim material is in any event too costly for use in disposable absorbent articles.
It is, therefore, an object of the present invention to provide a reinforced landing zone for the backsheet of a disposable absorbent article by utilizing a reinforcement member that is less expensive than a reinforcement member of synthetic polymer material.
It is a further object of this invention to provide a reinforcement member that is more resistant to heat, and therefore more suitable to be used with a hot melt adhesive than a reinforcement member made of a synthetic polymer material.
It is yet another object of the present invention to provide a reinforcement member that provides a suitable substrate for printing, and when printed provides better character definition for the indicia printed thereon than polyolefin materials.